feat: Add OpenRouter provider

src/Cellm/AddIn/CellmAddIn.cs

@@ -15,6 +15,7 @@
 using Cellm.Models.Providers.Ollama;
 using Cellm.Models.Providers.OpenAi;
 using Cellm.Models.Providers.OpenAiCompatible;
+using Cellm.Models.Providers.OpenRouter;
 using Cellm.Models.Resilience;
 using Cellm.Tools;
 using Cellm.Tools.FileReader;
@@ -83,6 +84,7 @@ private static ServiceCollection ConfigureServices(ServiceCollection services)
             .Configure<OllamaConfiguration>(configuration.GetRequiredSection(nameof(OllamaConfiguration)))
             .Configure<OpenAiConfiguration>(configuration.GetRequiredSection(nameof(OpenAiConfiguration)))
             .Configure<OpenAiCompatibleConfiguration>(configuration.GetRequiredSection(nameof(OpenAiCompatibleConfiguration)))
+            .Configure<OpenRouterConfiguration>(configuration.GetRequiredSection(nameof(OpenRouterConfiguration)))
             .Configure<ResilienceConfiguration>(configuration.GetRequiredSection(nameof(ResilienceConfiguration)))
             .Configure<SentryConfiguration>(configuration.GetRequiredSection(nameof(SentryConfiguration)));
 
@@ -166,7 +168,8 @@ private static ServiceCollection ConfigureServices(ServiceCollection services)
             .AddResilientHttpClient(resilienceConfiguration, cellmAddInConfiguration, Provider.DeepSeek)
             .AddResilientHttpClient(resilienceConfiguration, cellmAddInConfiguration, Provider.Gemini)
             .AddResilientHttpClient(resilienceConfiguration, cellmAddInConfiguration, Provider.Mistral)
-            .AddResilientHttpClient(resilienceConfiguration, cellmAddInConfiguration, Provider.OpenAiCompatible);
+            .AddResilientHttpClient(resilienceConfiguration, cellmAddInConfiguration, Provider.OpenAiCompatible)
+            .AddResilientHttpClient(resilienceConfiguration, cellmAddInConfiguration, Provider.OpenRouter);
 
 #pragma warning disable EXTEXP0018 // Type is for evaluation purposes only and is subject to change or removal in future updates.
         services
@@ -185,7 +188,8 @@ private static ServiceCollection ConfigureServices(ServiceCollection services)
             .AddMistralChatClient()
             .AddOllamaChatClient()
             .AddOpenAiChatClient()
-            .AddOpenAiCompatibleChatClient();
+            .AddOpenAiCompatibleChatClient()
+            .AddOpenRouterChatClient();
 
         // Add tools
         services
@@ -232,7 +236,8 @@ internal static IEnumerable<IProviderConfiguration> GetProviderConfigurations()
             Services.GetRequiredService<IOptionsMonitor<MistralConfiguration>>().CurrentValue,
             Services.GetRequiredService<IOptionsMonitor<OllamaConfiguration>>().CurrentValue,
             Services.GetRequiredService<IOptionsMonitor<OpenAiConfiguration>>().CurrentValue,
-            Services.GetRequiredService<IOptionsMonitor<OpenAiCompatibleConfiguration>>().CurrentValue
+            Services.GetRequiredService<IOptionsMonitor<OpenAiCompatibleConfiguration>>().CurrentValue,
+            Services.GetRequiredService<IOptionsMonitor<OpenRouterConfiguration>>().CurrentValue
         ];
     }
 

src/Cellm/AddIn/UserInterface/Ribbon/RibbonModelGroup.cs

@@ -12,6 +12,7 @@
 using Cellm.Models.Providers.Ollama;
 using Cellm.Models.Providers.OpenAi;
 using Cellm.Models.Providers.OpenAiCompatible;
+using Cellm.Models.Providers.OpenRouter;
 using Cellm.Users;
 using ExcelDna.Integration.CustomUI;
 using Microsoft.Extensions.AI;
@@ -494,6 +495,9 @@ public void ShowProviderSettingsForm(IRibbonControl control)
                 case Provider.OpenAiCompatible:
                     currentBaseAddress = GetProviderConfiguration<OpenAiCompatibleConfiguration>()?.BaseAddress?.ToString() ?? "";
                     break;
+                case Provider.OpenRouter:
+                    currentBaseAddress = GetProviderConfiguration<OpenRouterConfiguration>()?.BaseAddress?.ToString() ?? "";
+                    break;
                 default:
                     break;
             }

src/Cellm/Cellm.csproj

@@ -28,6 +28,7 @@
     <None Remove="AddIn\UserInterface\Resources\mistral.png" />
     <None Remove="AddIn\UserInterface\Resources\ollama.png" />
     <None Remove="AddIn\UserInterface\Resources\openai.png" />
+    <None Remove="AddIn\UserInterface\Resources\OpenRouter.svg" />
     <None Remove="appsettings.json" />
     <None Remove="appsettings.Local.json" />
   </ItemGroup>
@@ -90,5 +91,6 @@
     <EmbeddedResource Include="AddIn\UserInterface\Resources\Mistral.png" />
     <EmbeddedResource Include="AddIn\UserInterface\Resources\Ollama.png" />
     <EmbeddedResource Include="AddIn\UserInterface\Resources\OpenAi.png" />
+    <EmbeddedResource Include="AddIn\UserInterface\Resources\OpenRouter.svg" />
   </ItemGroup>
 </Project>

src/Cellm/Models/Providers/OpenRouter/OpenRouterConfiguration.cs

@@ -0,0 +1,35 @@
+using Cellm.Users;
+using Microsoft.Extensions.AI;
+
+namespace Cellm.Models.Providers.OpenRouter;
+
+internal class OpenRouterConfiguration : IProviderConfiguration
+{
+    public Provider Id { get => Provider.OpenRouter; }
+
+    public string Name { get => "OpenRouter"; }
+
+    public Entitlement Entitlement { get => Entitlement.EnableOpenRouterProvider; }
+
+    public string Icon { get => $"AddIn/UserInterface/Resources/{nameof(Provider.OpenRouter)}.svg"; }
+
+    public Uri BaseAddress => new("https://openrouter.ai/api/v1");
+
+    public string DefaultModel { get; init; } = string.Empty;
+
+    public string ApiKey { get; init; } = string.Empty;
+
+    public string SmallModel { get; init; } = string.Empty;
+
+    public string MediumModel { get; init; } = string.Empty;
+
+    public string LargeModel { get; init; } = string.Empty;
+
+    public AdditionalPropertiesDictionary? AdditionalProperties { get; init; } = [];
+
+    public bool SupportsJsonSchemaResponses { get; init; } = true;
+
+    public bool SupportsStructuredOutputWithTools { get; init; } = true;
+
+    public bool IsEnabled { get; init; } = false;
+}

src/Cellm/Models/Providers/Provider.cs

@@ -11,5 +11,6 @@ public enum Provider
     Mistral,
     Ollama,
     OpenAi,
-    OpenAiCompatible
+    OpenAiCompatible,
+    OpenRouter
 }

src/Cellm/Models/ServiceCollectionExtensions.cs

@@ -21,6 +21,7 @@
 using Cellm.Models.Providers.Ollama;
 using Cellm.Models.Providers.OpenAi;
 using Cellm.Models.Providers.OpenAiCompatible;
+using Cellm.Models.Providers.OpenRouter;
 using Cellm.Models.Resilience;
 using Cellm.Users;
 using Microsoft.Extensions.AI;
@@ -426,6 +427,37 @@ public static IServiceCollection AddOpenAiCompatibleChatClient(this IServiceColl
         return services;
     }
 
+    public static IServiceCollection AddOpenRouterChatClient(this IServiceCollection services)
+    {
+        services
+            .AddKeyedChatClient(Provider.OpenRouter, serviceProvider =>
+            {
+                var account = serviceProvider.GetRequiredService<Account>();
+                account.ThrowIfNotEntitled(Entitlement.EnableOpenRouterProvider);
+
+                var openRouterConfiguration = serviceProvider.GetRequiredService<IOptionsMonitor<OpenRouterConfiguration>>();
+                var resilientHttpClient = serviceProvider.GetResilientHttpClient(Provider.OpenRouter);
+
+                if (string.IsNullOrWhiteSpace(openRouterConfiguration.CurrentValue.ApiKey))
+                {
+                    throw new CellmException($"Empty {nameof(OpenRouterConfiguration.ApiKey)} for {Provider.OpenRouter}. Please set your API key.");
+                }
+
+                var openAiClient = new OpenAIClient(
+                    new ApiKeyCredential(openRouterConfiguration.CurrentValue.ApiKey),
+                    new OpenAIClientOptions
+                    {
+                        Transport = new HttpClientPipelineTransport(resilientHttpClient),
+                        Endpoint = openRouterConfiguration.CurrentValue.BaseAddress
+                    });
+
+                return openAiClient.GetChatClient(openRouterConfiguration.CurrentValue.DefaultModel).AsIChatClient();
+            }, ServiceLifetime.Transient)
+            .UseFunctionInvocation();
+
+        return services;
+    }
+
     public static IServiceCollection AddTools(this IServiceCollection services, params Delegate[] tools)
     {
 

src/Cellm/Users/Entitlement.cs

@@ -14,6 +14,7 @@ public enum Entitlement
     EnableOpenAiCompatibleProvider,
     EnableOpenAiCompatibleProviderLocalModels,
     EnableOpenAiCompatibleProviderHostedModels,
+    EnableOpenRouterProvider,
     EnableModelContextProtocol,
     DisableTelemetry
 }

src/Cellm/Users/Models/Entitlements.cs

@@ -22,7 +22,8 @@ internal class Entitlements()
         Entitlement.EnableOllamaProvider,
         Entitlement.EnableOpenAiProvider,
         Entitlement.EnableOpenAiCompatibleProvider,
-        Entitlement.EnableOpenAiCompatibleProviderLocalModels
+        Entitlement.EnableOpenAiCompatibleProviderLocalModels,
+        Entitlement.EnableOpenRouterProvider
     ];
 
     public IEnumerable<Entitlement> AsEnumerable()

src/Cellm/appsettings.json

@@ -102,6 +102,14 @@
         "ApiKey": "",
         "IsEnabled": true
     },
+    "OpenRouterConfiguration": {
+        "DefaultModel": "mistralai/mistral-small-3.2-24b-instruct",
+        "ApiKey": "",
+        "SmallModel": "mistralai/mistral-small-3.2-24b-instruct",
+        "MediumModel": "google/gemini-2.5-flash",
+        "LargeModel": "anthropic/claude-opus-4-5-20251101",
+        "IsEnabled": true
+    },
     "ModelContextProtocolConfiguration": {
         "StdioServers": [
             {